Discuss the role of wastewater reuse and desalination in reconciling industrial growth with groundwater sustainability in water-stressed States.

Tamil Nadu ranks 3rd on NITI Aayog's Investment Friendliness Index 2026 [1]. Yet a CGWB profile lists 374 over-exploited and 48 critical groundwater blocks in the State [2]. Wastewater reuse and desalination can separate industrial demand from aquifers, but they work only alongside pricing, siting and enforcement.

Role of wastewater reuse

• Freshwater substitution: treated sewage and recycled effluent can meet industry's process and cooling needs. This keeps groundwater for drinking and farming.
• Pollution control: in Tiruppur, after litigation by Noyyal farmers, the Madras High Court ordered polluting dyeing units closed. The pollution board then required RO-based Zero Liquid Discharge (ZLD) [4].
• Cluster model: CETPs with RO and reject-management systems were commissioned by 2010 [5]. Shared plants make ZLD affordable for small units.

Role of desalination

• New supply for coastal belts: Chennai's Minjur and Nemmeli seawater RO plants add 100 MLD each [6][7]. This eases pressure on aquifers.
• Rain-independent: it gives a reliable supply during droughts and monsoon failures.

Limitations

• Energy-intensive: both technologies turn a water problem into a power bill, which is hardest on MSMEs.
• Brine and reject: these harm coastal ecology. Landlocked districts have no sea outlet, so the reject must be stored on land.
• Geography: desalination is uneconomic for interior rain-shadow districts, where stress is highest.
• Cheap groundwater: while borewell water is almost free, recycled water cannot compete on cost.
• Compliance gaps: ZLD claimed on paper often differs from ZLD on the ground, so continuous monitoring is needed.

Way forward

• Site water-intensive units (textiles, leather, chemicals) using CGWB's firka-level 2024 assessment [3] and NAQUIM aquifer maps.
• Build a CETP and reuse pipelines into every new industrial park, with online effluent monitoring.
• Price industrial extraction in over-exploited units so that reuse becomes the cheaper option.
• Run desalination on renewable power and set standards for brine discharge.
• Pair the investment index with sustainability indicators such as NITI's Composite Water Management Index.

Reuse and desalination expand the water available to industry without drawing down aquifers, but they are not a substitute for demand management. Combined with groundwater pricing, aquifer-based siting and strict enforcement, they can make investment competitiveness compatible with SDG 6 and the Article 21 right to water. That would let water-stressed States grow without depleting future users' share.